From the sea of Legos to the leaning towers of sippy cups, your child's endless belongings are often tougher to tame than she is. Time for some spring-cleaning—with the help of a one Marie Kondo. Yup, turns out those same life-changing tidying principles that saved your closet in 2015 can also take your kid's stuff from deranged mess to calm and collected. Here, five invaluable decluttering lessons.